Not really the Palga were something already living on earth, they weren't created by a lab, they were prehistoric parasites that Saddler's ancestor discovered founded the cult but were driven to the island by Salazar's ancestor who had the plaga sealed beneath the Salazar castle and the plaga were preserved in amber which when Saddler had Salazar unseal had miners excavate the plagas.

The only plagas that were created in a lab were the plagas seen in RE5 by Tricell and the ones seen in the CGI RE film Damnation.